15.11.2014

NB: We use cookies to help personalise your web experience and comply with Irish healthcare law. This site contains information, news and advice for healthcare professionals.You have informed us that you are not a healthcare professional and therefore we are unable to provide you with access to this site. The new recommendations advise adapting treatment to each patient’s situation, including history, wishes, and willingness to make lifestyle changes. Actual treatment targets which are now emphasised are patient-oriented outcomes, in general related to micro- and macrovascular events (e.g. The first and most widely used medical treatment is metformin, a biguanide whose mechanism of action predominately involves reducing hepatic glucose production.
If the HbA1c target is not achieved after ?3 months, there are five drug choices including a second oral agent (sulfonylurea, TZD, or DPP-4 inhibitor), a GLP-1 receptor agonist, or basal insulin (see general algorithm).
Because there has been no good quality study comparing all available treatment strategies, there is no clear-cut decision tree as there was in the previous hyperglycaemia guidelines, and shared decision making with the patient is important to help in the selection of therapeutic option. On average, any second agent is typically associated with a further reduction in HbA1c of approximately 1%.
Evidence suggests that there is some advantage in adding a third noninsulin agent to a two-drug combination not achieving the glycaemic target.
In using triple combinations the essential consideration is obviously to use agents with complementary mechanisms of action. Diet, exercise, and education remain the foundation of all type 2 diabetes treatment programmes. After metformin, though data are more limited, it is reasonable to consider combination therapy with an additional 1-2 oral or injectable agents with the objective of minimising side effects where possible. For many patients insulin therapy alone or in combination with other agents will ultimately be required to maintain glucose control. All treatment decisions, where possible, should take into account the patient’s preferences, needs, and values.
Reference: [adapted] Position Statement of the American Diabetes Association and the European Association for the Study of Diabetes.
Do you agree that private hospitals should be paid via the NTPF to cut public hospital waiting lists? Originally, monogenic inherited diseases (those caused by inherited single gene defects), such as cystic fibrosis, were considered primary targets for gene therapy. While the positive therapeutic outcome was celebrated as a breakthrough for gene therapy, a serious drawback subsequently became evident. A small number of more recent gene therapy clinical trials, however, are concerned with monogenic disorders. Gene therapy relies on similar principles as traditional pharmacologic therapy; specifically, regional specificity for the targeted tissue, specificity of the introduced gene function in relation to disease, and stability and controllability of expression of the introduced gene. Gene therapy can be performed either by direct transfer of genes into the patient or by using living cells as vehicles to transport the genes of interest. A major disadvantage, however, is the additional biological complexity brought into systems by living cells.
After in vitro manipulation, these cells may be retransplanted into patients by injection into the bloodstream, where they travel automatically to the place in the bone marrow in which they are functionally active. The traditional method to introduce a therapeutic gene into hematopoietic stem cells from bone marrow or peripheral blood involves the use of a vector derived from a certain class of virus, called a retrovirus.
The major drawback of these methods is that the therapeutic gene frequently integrates more or less randomly into the chromosomes of the target cell. Another major limitation of using adult stem cells is that it is relatively difficult to maintain the stem cell state during ex vivo manipulations. Embryonic stem cells are capable of unlimited self-renewal while maintaining the potential to differentiate into derivatives of all three germ layers. Murine (mouse) embryonic stem cells were isolated over 20 years ago,12,13 and paved the way for the isolation of nonhuman primate, and finally human embryonic stem cells.14 Much of the anticipated potential surrounding human embryonic stem cells is an extrapolation from pioneering experiments in the mouse system.
Following derivation, human embryonic stem cells are easily accessible for controlled and specific genetic manipulation. First, human embryonic stem cells could be genetically manipulated to introduce the therapeutic gene. An important parameter that must be carefully monitored is the random integration into the host genome, since this process can induce mutations that lead to malignant transformation or serious gene dysfunction. Homologous recombination is a very rare event in cells, and thus a powerful selection strategy is necessary to identify the cells in which it occurs. Gene targeting by homologous recombination has recently been applied to human embryonic stem cells.22 This is important for studying gene functions in vitro for lineage selection and marking. Despite promising scientific results with genetically modified stem cells, some major problems remain to be overcome.
The addition of human embryonic stem cells to the experimental gene therapy arsenal offers great promise in overcoming many of the existing problems of cellular based gene therapy that have been encountered in clinic trials (see Figure 4.3). These much-anticipated new treatment guidelines rely on a more individualised approach, and not as much on a strict glycated haemoglobin (HbA1c) target. The choice is based on patient and drug characteristics – including willingness to self-inject or need for weight loss – with the over-riding goal of improving glycaemic control while minimising side effects. Reconsider the approach promptly if it proves to be unsuccessful, as months of uncontrolled hyperglycaemia should specifically be avoided. Since diabetes is associated with progressive ?-cell loss, many patients, especially those with long-standing disease, will ultimately need to be transitioned to insulin. Its emergence is a direct consequence of the revolution heralded by the introduction of recombinant DNA methodology in the 1970s.
For instance, in pioneering studies on the correction of adenosine deaminase deficiency, a lymphocyte-associated severe combined immunodeficiency (SCID), was attempted.1 Although no modulation of immune function was observed, data from this study, together with other early clinical trials, demonstrated the potential feasibility of gene transfer approaches as effective therapeutic strategies. Out of the approximately 1000 recorded clinical trials (January 2005), fewer than 10% target these diseases (see Figure 4.1).
To integrate all these aspects into a successful therapy is an exceedingly complex process that requires expertise from many disciplines, including molecular and cell biology, genetics and virology, in addition to bioprocess manufacturing capability and clinical laboratory infrastructure.
In this scenario, genes are delivered directly into a patient's tissues or bloodstream by packaging into liposomes (spherical vessels composed of the molecules that form the membranes of cells) or other biological microparticles. In many cases, direct gene transfer does not allow very sophisticated control over the therapeutic gene.

This procedure is relatively complex in comparison to direct gene transfer, and can be divided into three major steps.
Isolation of a specific cell type requires not only extensive knowledge of biological markers, but also insight into the requirements for that cell type to stay alive in vitro and continue to divide. The role of adult stem cells is to sustain an established repertoire of mature cell types in essentially steady-state numbers over the lifetime of the organism. One type of retroviral vector was initially employed to show proof-of-principle that a foreign gene (in that instance the gene was not therapeutic, but was used as a molecular tag to genetically mark the cells) introduced into bone marrow cells may be stably maintained for several months.9 However, these particular retroviral vectors were only capable of transferring the therapeutic gene into actively dividing cells. In principle, this is dangerous, because the gene therapy vector can potentially modify the activity of neighboring genes (positively or negatively) in close proximity to the insertion site or even inactivate host genes by integrating into them. Even after months and years of growth in the laboratory, they retain the ability to form any cell type in the body. Experiments performed with human embryonic stem cells in the last couple of years indicate that these cells have the potential to make an important impact on medical science, at least in certain fields. When this facility is combined with their rapid growth, remarkable stability, and ability to mature in vitro into multiple cell types of the body, human embryonic stem cells are attractive potential tools for gene therapy. This gene may either be active or awaiting later activation, once the modified embryonic stem cell has differentiated into the desired cell type. The levels of immune system reconstitution observed in the mice were quite modest (<1% of normal), while the methodology employed to achieve hematopoietic engraftment is not clinically feasible.
Since these cells can be differentiated in vitro into many cell types, including presumably tissue-specific stem cells, they may provide a constant in vitro source of cellular material. However, several copies of the therapeutic gene may also be integrated into the genome, helping to bypass positional effects and gene silencing. Specific proteins stabilizing these episomal DNA molecules have been identified as well as viruses (adenovirus) that persist stably for some time in an episomal condition. Recombinant DNA is altered in vitro, and the therapeutic gene is introduced into a copy of the genomic DNA that is targeted during this process.
Usually, the introduced construct has an additional gene coding for antibiotic resistance (referred to as a selectable marker), allowing cells that have incorporated the recombinant DNA to be positively selected in culture. For therapeutic applications in transplantation medicine, the controlled modification of specific genes should be useful for purifying specific embryonic stem cell-derived, differentiated cell types from a mixed population, altering the antigenicity of embryonic stem cell derivatives, and adding defined markers that allow the identification of transplanted cells. The more specific and extensive the genetic modification, the longer the stem cells have to remain in vitro. Transgenic genes, as well as vectors introducing these genes (such as those derived from viruses), potentially trigger immune system responses. Further research is essential to determine the full potential of both adult and embryonic stem cells in this exciting new field. Molecular analysis of T lymphocyte-directed gene therapy for adenosine deaminase deficiency: long-term expression in vivo of genes introduced with a retroviral vector.
A serious adverse event after successful gene therapy for X-linked severe combined immunodeficiency. Correction of ADA-SCID by stem cell gene therapy combined with nonmyeloablative conditioning. Non-hematopoietic bone marrow stem cells: molecular control of expansion and differentiation.
Gene marking to determine whether autologous marrow infusion restores long-term haemopoiesis in cancer patients.
Isolation of a pluripotent cell line from early mouse embryos cultured in medium conditioned by teratocarcinoma stem cells. Correction of a genetic defect by nuclear transplantation and combined cell and gene therapy.
Lack of expression from a retroviral vector after transduction of murine hematopoietic stem cells is associated with methylation in vivo. High-level sustained transgene expression in human embryonic stem cells using lentiviral vectors. Functional gene screening in embryonic stem cells implicates Wnt antagonism in neural differentiation. HoxB4 confers definitive lymphoid-myeloid engraftment potential on embryonic stem cell and yolk sac hematopoietic progenitors.
HbA1c) generally reflect changes in the probability of developing microvascular disease but not necessarily macrovascular complications. On the basis of findings from ACCORD and other studies, the guidelines set the HbA1c goal at 7% in general, but with some individualisation (e.g.
It lowers blood sugar levels and may help reduce cardiovascular risk without increased risk of hypoglycaemia and weight gain. Gene therapy is still highly experimental, but has the potential to become an important treatment regimen.
The majority of current clinical trials (66% of all trials) focus on polygenic diseases, particularly cancer.
Alternately, the genes are packaged into genetically-engineered viruses, such as retroviruses or adenoviruses. This is because the transferred gene either randomly integrates into the patient's chromosomes or persists unintegrated for a relatively short period of time in the targeted tissue. In the first step, cells from the patient or other sources are isolated and propagated in the laboratory. Unfortunately, specific biological markers are not known for many cell types, and the majority of normal human cells cannot be maintained for long periods of time in vitro without acquiring deleterious mutations.
Although adult tissues with a high turnover rate, such as blood, skin, and intestinal epithelium, are maintained by tissue-specific stem cells, the stem cells themselves rarely divide.
These properties reflect their origin from cells of the early embryo at a stage during which the cellular machinery is geared toward the rapid expansion and diversification of cell types. In particular, this impact includes: a) differentiation of human embryonic stem cells into various cell types, such as neurons, cardiac, vascular, hematopoietic, pancreatic, hepatic, and placental cells, b) the derivation of new cell lines under alternative conditions, c) and the establishment of protocols that allow the genetic modification of these cells. Two possible scenarios whereby human embryonic stem cells may benefit the gene therapy field are discussed below.
Recently published reports establish the feasibility of such an approach.15 Skin cells from an immunodeficient mouse were used to generate cellular therapy that partially restored immune function in the mouse.
This methodology involved using a more severely immunodeficient mouse as a recipient (which also had the murine equivalent of the human X-linked SCID mutation) and genetically engineering the hematopoietic engrafting cells with a potential oncogene prior to transplantation.

Positional effects are caused by certain areas within the genome and directly influence the activity of the introduced gene.
Next, recombinant DNA is introduced by transfection into the cell, where it recombines with the homologous part of the cell genome. However, antibiotic resistance only reveals that the cells have taken up recombinant DNA and incorporated it somewhere in the genome.
Additionally, since the therapeutic gene can now be introduced into defined regions of the human genome, better controlled expression of the therapeutic gene should be possible. Although human embryonic stem cells in the culture dish remain remarkably stable, the cells may accumulate genetic and epigenetic changes that might harm the patient (epigenetic changes regulate gene activity without altering the genetic blueprint of the cell). If stem cells are not autologous, they eventually cause immuno-rejection of the transplanted cell type. The downside of using aggressive treatment to decrease HbA1c is the risk for complications associated with hypoglycaemia, as patients with hypoglycaemia have higher risks for almost all outcomes, including micro- and macrovascular outcomes. However, metformin is associated with initial GI side effects, and caution is also advised to avoid its use in patients at risk for lactic acidosis (e.g. In principle, it allows the transfer of genetic information into patient tissues and organs. Because of biosafety concerns, the viruses are typically altered so that they are not toxic or infectious (that is, they are replication incompetent).
Additionally, the targeted organ or tissue is not always easily accessible for direct application of the therapeutic gene.
Second, the therapeutic gene is introduced into these cells, applying methods similar to those used in direct gene transfer. However, in certain situations, such as during tissue repair after injury or following transplantation, stem cell divisions may become more frequent. Vectors derived from other types of retroviruses (lentiviruses) and adenoviruses have the potential to overcome this limitation, since they also target non-dividing cells. In these experiments, embryonic stem cells were generated from an immunodeficient mouse by nuclear transfer technology. Usually, small molecules, such as liposomes, as well as other cationic-lipid based particles are employed to facilitate the entry of DNA encoding the gene of interest into the cells.
Gene silencing refers to the phenomenon whereby over time, most artificially introduced active genes are turned off by the host cell, a mechanism that is not currently well understood. This in turn results in the replacement of normal genomic DNA with recombinant DNA containing genetic modifications. To select for cells in which homologous recombination has occurred, the end of the recombination construct often includes the thymidine kinase gene from the herpes simplex virus. Indeed, sporadic chromosomal abnormalities in human embryonic stem cell culture have been reported, and these may occur more frequently when the cells are passaged as bulk populations. These basic tools of gene therapists have been extensively optimized over the past 10 years. The prototypic example of adult stem cells, the hematopoietic stem cell, has already been demonstrated to be of utility in gene therapy.4,5 Although they are relatively rare in the human body, these cells can be readily isolated from bone marrow or after mobilization into peripheral blood. The nucleus of an egg cell was replaced with that from a skin cell of an adult mouse with the genetic immunodeficiency. Additionally, some viruses (particularly retroviruses) only infect dividing cells effectively, whereas others (lentiviruses) do not require actively dividing cells. In these cases, integration of several copies may help to achieve stable gene expression, since a subset of the introduced genes may integrate into favorable sites. Cells that randomly incorporate recombinant DNA usually retain the entire DNA construct, including the herpes virus thymidine kinase gene. This observation reinforces the necessity to optimize culture conditions further, to explore new human embryonic stem cell lines, and to monitor the existing cell lines.23,24 Additionally undifferentiated embryonic stem cells have the potential to form a type of cancer called a teratocarcinoma. Furthermore, the procedure allows the addition of new functions to cells, such as the production of immune system mediator proteins that help to combat cancer and other diseases. Specific surface markers allow the identification and enrichment of hematopoietic stem cells from a mixed population of bone marrow or peripheral blood cells. All of these techniques have been applied to various stem cells, including human embryonic stem cells. In most cases, the genetic information carried by the viral vector is stably integrated into the host cell genome (the total complement of chromosomes in the cell). In cells that display homologous recombination between the recombinant construct and cellular DNA, an exchange of homologous DNA sequences is involved, and the non-homologous thymidine kinase gene at the end of the construct is eliminated. Safety precautions are therefore necessary, and currently, protocols are being developed to allow the complete depletion of any remaining undifferentiated embryonic stem cells.25 This may be achieved by rigorous purification of embryonic stem cell derivatives or introducing suicide genes that can be externally controlled. In the laboratory dish (in vitro), cells can be manipulated much more precisely than in the body (in vivo). However, the destiny of the introduced DNA is relatively poorly controlled using these procedures. Cells expressing the thymidine kinase gene are killed by the antiviral drug ganciclovir in a process known as negative selection. Some of the cell types that continue to divide under laboratory conditions may be expanded significantly before reintroduction into the patient. In most cells, the DNA disappears after days or weeks, and in rare cases, integrates randomly into host chromosomal DNA. Therefore, those cells undergoing homologous recombination are unique in that they are resistant to both the antibiotic and ganciclovir, allowing effective selection with these drugs (see Figure 4.2). Moreover, some cell types are able to localize to particular regions of the human body, such as hematopoietic (blood-forming) stem cells, which return to the bone marrow. In principle, this approach may be employed for treating human patients with immunodeficiency or other diseases that may be corrected by cell transplantation.